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Showing papers in "Smart Materials and Structures in 1995"


Journal ArticleDOI
TL;DR: In this article, a new adaptive sandwich structure is constructed using the shear mode of piezoelectric materials, and a comparative study of the sandwich structure and the corresponding surface-mounted actuation structure is performed using finite-element analysis.
Abstract: A new adaptive sandwich structure is constructed using the shear mode of piezoelectric materials. A comparative study of the sandwich structure and the corresponding surface-mounted actuation structure is performed using finite-element analysis. The effects of actuator length and location on actuation performance of the structures are studied. The stress distributions under mechanical and electrical loads are investigated for both the sandwich beam and the surface-mounted actuation beam. It is shown that the stress level within the actuators is more severe for the surface-mounted actuation beam than for the sandwich. Also, the interface-stress distribution between actuator and host structure is analysed. It is shown that sandwich construction offers many advantages over conventional surface-mounted actuation constructions.

131 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used active control and passive damping to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composite structure.
Abstract: The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure in such a way as to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composite structure. The results have indicated that this concept of active damping produces very effective levels of vibration suppression. In the case of cantilever beams the vibration levels in the first two modes can be almost eliminated when velocity feedback of the beam tip is used. The results show that the addition of active control and passive damping in a single structure combines the advantages of passive damping in the higher modes and active control in the lower modes. In addition active damping as defined in this paper produces a fail-safe mechanism in case of instability occurring in the feedback loop since a considerable level of passive damping is always present.

120 citations


Journal ArticleDOI
TL;DR: In this paper, a combined theoretical/experimental study of the heat transfer in thermoelectric shape memory alloy (SMA) actuators is undertaken, where a one-dimensional model is developed and transient temperatures in the SMA are evaluated for different applied electric current densities.
Abstract: A combined theoretical/experimental study of the heat transfer in thermoelectric shape memory alloy (SMA) actuators is undertaken in this paper. A one-dimensional model of a thermoelectric unit cell with a SMA junction is developed first and the transient temperatures in the SMA are evaluated for different applied electric current densities. As a first step towards the design of an actuator, a thermoelectric module is assembled in the laboratory for cooling/heating the SMA. Transient temperature profiles are recorded for the monotonic heating and cooling runs for two different materials-copper and SMA (with or without the phase transformation). These recorded profiles are then compared with the predictions from the model; the agreement is reasonable, particularly during the cooling process. Temperature profiles are also recorded for cyclic cooling and heating of copper at a frequency of 0.5 Hz and a good comparison is obtained. Theoretical predictions for thermal cycling of SMA show that it is possible to achieve a frequency of 2 Hz on full phase transformation and 17 Hz on partial transformation of 25%.

109 citations


Journal ArticleDOI
TL;DR: In this article, a beam constrained by shape memory wires is modeled as a pseudoelastic hysteresis loop and modal analysis is used to obtain the dynamic response of the system.
Abstract: Experimental results on the dynamics of a beam constrained by shape memory wires are presented. It is observed that the damping increases significantly when the shape memory wires are stressed such that they lie within the pseudoelastic hysteresis loop. Theoretical models of the inner hysteresis loop are considered, and modal analysis is used to obtain the dynamic response of the system. Simulations of the system using these models give theoretical values of damping which agree well with those observed experimentally. The proposed models of the pseudoelastic hysteresis loop are adequate for providing an estimate of the initial increase of damping due to the use of prestressed shape memory wires in structures. These results demonstrate that pseudoelasticity of shape memory wires can be used to augment passive damping significantly in structural systems.

89 citations


Journal ArticleDOI
TL;DR: In this paper, a new class of strain sensors for short-fiber composites is proposed, based on the electrical resistance change accompanying the reversible pull-out of conducting short fibers in a less conducting matrix.
Abstract: A new class of strain sensors has been discovered. These sensors are short-fiber composites. Their sensing ability is based on the electrical resistance change accompanying the reversible pull-out of conducting short fibers in a less conducting matrix. The fiber pull-out is associated with crack opening; the fiber push-in is associated with crack closing. The fiber pull-out, though slight, causes an increase in the fiber-matrix contact resistivity, thereby increasing the overall resistance of the composite. An example of these sensors is carbon fiber reinforced concrete.

86 citations


Journal ArticleDOI
TL;DR: In this article, the effect of training conditions, bias stress and extended thermal cycling on the transformational behavior of thin wires (0.19 mm diameter) was investigated to determine their two-way shape memory.
Abstract: Shape memory alloys (SMA) are a class of materials proposed to be used as actuator elements in smart structures. They undergo a reversible martensitic phase transformation during thermal cycling. In this work, 55-nitinol (55% nickel-45% titanium shape memory alloy) was investigated to determine the effect of training conditions, bias stress and extended thermal cycling on the transformational behavior. Thin wires (0.19 mm diameter) were trained using a previously developed methodology to exhibit two-way shape memory (TWSM). The wires were placed in a cryogenically cooled apparatus and heated by electrical resistance while the wire deformation was measured. Several different training schedules were used by varying the amount of prestrain and number of training cycles. The recovery strain and transformation temperatures were measured throughout extended thermal cycling (up to 10000 cycles). A bias stress was also used to enhance the amount of retention of prestrain in the wires. In all cases, stabilization of TWSM behavior occurred within 2000 thermal cycles.

82 citations


Journal ArticleDOI
TL;DR: In this paper, an intensity-based optical fiber sensor was designed and evaluated under tension/tension and tension/compression fatigue loading conditions, and the feasibility of using the embedded sensor for fatigue damage detection was demonstrated.
Abstract: The detection of fatigue-induced damage within fibre-reinforced composite materials is of vital importance in areas where these materials are used for critical load-bearing applications. Embedded fibre-optic sensors are suitable for damage detection in composite materials because they can be easily integrated into the structure with minimal interference with the bulk properties of the composite. In this current study, a novel intensity-based optical fibre sensor was designed and evaluated under tension/tension and tension/compression fatigue loading conditions. This intensity sensor has the ability to monitor rapid strain changes without loss of the reference level. Furthermore, this sensor utilizes relatively simple and inexpensive instrumentation. The fibre-optic strain sensor was embedded within a 16-ply 0/90 carbon/epoxy laminate at the manufacturing stage. The embedded optical fibre sensor was not found to affect the fatigue life of the composite both under tension/tension and tension/compression loading. The feasibility of using the embedded sensor for fatigue damage detection was demonstrated. Excellent correlation was also obtained between the strain data from a surface mounted optical fibre sensor and a surface-mounted extensometer under fatigue loading conditions.

69 citations


Journal ArticleDOI
TL;DR: In this article, a composite piezoresistive material was found to be piezoreistive strain sensor, such that the magnitude of the reversible fractional increase in electrical resistance per unit strain was 6-23 under tension and 29-31 under compression.
Abstract: Epoxy containing 5.5 vol.% short carbon fibers was found to be piezoresistive strain sensor, such that the magnitude of the reversible fractional increase in electrical resistance per unit strain was 6-23 under tension and 29-31 under compression. These values are much higher than those of previously reported composite piezoresistive materials. The reversible fractional increase in resistance was positive under tension and negative under compression, but the irreversible fractional increase in resistance was positive under both tension and compression. Both reversible and irreversible fractional increases in resistance increased in magnitude with increasing stress/strain amplitude. The reversible portion was due to piezoresistivity, while the irreversible portion was due to damage.

59 citations


Journal ArticleDOI
TL;DR: In this article, a two-span concrete highway bridge built in the city of Calgary in 1993 is the first in the world to use carbon fiber composite prestressing tendons in several of its precast concrete deck support girders.
Abstract: Carbon fiber based composite material is of considerable interest for the replacement of steel in large concrete structures, such as bridges, where corrosion is a serious problem. A new two-span concrete highway bridge built in the city of Calgary in 1993 is the first in the world to use carbon fiber composite prestressing tendons in several of its precast concrete deck support girders. We have instrumented a number of these girders with an array of fiber optic intracore Bragg grating sensors in order to monitor the changes in the internal strain that take place over an extended period of time. A four-channel fiber laser demodulation system was developed for interrogating the set of Bragg grating sensors embedded within the bridge girders. This demodulation system was demonstrated to be rugged, compact and transportable to the bridge construction site where it allowed changes in the internal strain on all three types of prestressing tendon (steel and two types of carbon fiber composite) to be tracked over several months. The same set of structurally integrated Bragg grating sensors has also been used to measure the change in the internal strain within the deck girders arising from both static and dynamic loading of the bridge with a 21 ton truck. This first permanent testbed for structurally integrated Bragg grating sensors demonstrates the feasibility of building into new bridges fiber optic long-term structural monitoring sensing technology that will allow the use of these advanced composite materials to be monitored in a manner not previously practical. The strain information available from this type of monitoring system will assist engineers in their assessment of new materials and innovative design features, and has a potential role in maintenance and repair activities.

57 citations


Journal ArticleDOI
TL;DR: In this paper, an active truss element and control law is used along with a compressible fluid in order to dissipate energy during the motion of the structure, but the energy is not absorbed in the same manner as conventional viscous damper.
Abstract: In order to meet the demands of simplicity and reliability in active control systems for flexible structures, an inexpensive active truss element and control law has been developed in this research. A decentralized switching control law is used along with a compressible fluid in the truss element in order to dissipate energy during the motion of the structure. However, the energy is not absorbed in the same manner as a conventional viscous damper. The truss element retains its maximum stiffness, but has a reset-able nominal unstressed length. Energy is absorbed in the working fluid of the truss element through heat transfer to the environment when the nominal length is reset at the proper switching times. The control law is insensitive to changes in structural parameters such as mass, stiffness, and damping. In this paper, a mathematical model for the system is presented along with a stability analysis and experimental results.

53 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a technique for effective detection and location of impacts in metals and graphite/epoxy composite laminates, which employs the highly sensitive extrinsic Fabry-Perot interferometric (EFPI) optical fiber-based sensing system for recording the differential arrival times of impactgenerated acoustic signals using a set of four sensors whose location is predetermined.
Abstract: We present a novel technique for effective detection and location of impacts in metals and graphite/epoxy composite laminates. This scheme employs the highly sensitive extrinsic Fabry-Perot interferometric (EFPI) optical fiber-based sensing system for recording the differential arrival times of impact-generated acoustic signals using a set of four sensors whose location is predetermined. The sensors are surface-mounted on an aluminum sample and completely embedded in the composite specimen. A mathematical model is coded into a computer program to enable real-time, online determination of impact locations. The precise location of the impact can be deduced typically with a 0.5 mm resolution and an accuracy better than 5 mm. An improvement in the sensitivity of this system is proposed by using high-finesse Fabry-Perot cavities which modify the output transfer function curve of the sensor.

Journal ArticleDOI
TL;DR: In this paper, the performance and reliability of the fiber-optic-based extrinsic Fabry-Perot interferometric (EFPI) strain sensor is reported.
Abstract: Progress in the performance and reliability of the fiber-optic-based extrinsic Fabry-Perot interferometric (EFPI) strain sensor is reported. The developments include refined fabrication techniques and improved quality of constituent elements for enhanced durability and greater temperature sustenance, higher strain sensitivity using using high-finesse cavities, a modified sensor-head for complete strain-field characterization, absolute, real-time and inexpensive measurements employing white light interferometry and multipoint, distributed sensing using CDMA and path matching multiplexing techniques. It is shown that these improvements have assisted in overcoming the limitations of the conventional EFPI sensor and made possible the large-scale commercialization of the state-of-the-art EFPI-based strain sensing system.

Journal ArticleDOI
TL;DR: In this paper, a finite element model is developed for the active control of thermally induced vibration of laminated composite plates with piezoelectric sensors and actuators, taking into account the mass, stiffness and thermal expansion of the PAs.
Abstract: A finite-element model is developed for the active control of thermally induced vibration of laminated composite plates with piezoelectric sensors and actuators. The present model takes into account the mass, stiffness and thermal expansion of the piezoelectric patches. A C0 continuous nine-noded shear flexible element is implemented to model the plate. The piezoelectric sensing layer monitors the structural oscillation due to the direct piezoelectric effect and the actuator suppresses the oscillation via the converse piezoelectric effect. These two effects are then coupled with a constant gain feedback control algorithm to actively control the dynamic response of the plate in a closed loop. Numerical results indicate that thermally induced deformation of a laminated plate can be suppressed through the application of electrical potential to the piezoelectric patches.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated three types of carbon fiber tows used in CFGFRP composites and observed a very clear and significant change in electrical resistance at the transition point where the tows fractured, and found that this point could be easily controlled through the use of carbon fibers with different ultimate elongation values.
Abstract: Carbon fiber glass fiber reinforced plastic (CFGFRP) is used in concrete structures as a reinforcement material. Appropriate materials design indicates that CFGFRP should be a hybrid of a conductive material with a small ultimate elongation value and an insulating material with a large ultimate elongation value. In the present study, we evaluated three types of carbon fiber tows used in CFGFRP composites. We observed a very clear and significant change in electrical resistance at the transition point where carbon fiber tows fractured, and found that this point could be easily controlled through the use of carbon fibers with different ultimate elongation values. The electrical resistance characteristics of CFGFRP-reinforced concrete change along with changing loads. Furthermore, a permanent residual electrical resistance could be observed after the removal of load, and its change was dependent on the maximum load applied. The information on the fracture position was obtained by the arrangement of the CFGFRP composites. Monitoring changes in electrical resistance during and after loading is thus a promising method for anticipating the fracture of CFGFRP-reinforced concrete.

Journal ArticleDOI
TL;DR: In this paper, the performance of short-gage-length optical fiber sensors embedded in a reinforced concrete specimen was evaluated using a steel-reinforced concrete cross-beam specimen.
Abstract: This paper reports the performance of short-gage-length optical fiber sensors embedded in a reinforced concrete specimen. Embedded extrinsic Fabry-Perot optical fiber sensors, attached to steel reinforcement rods, were used to monitor local displacements and strain in a concrete cross-beam specimen. The strain data obtained from the fiber sensors were compared with data obtained from collocated foil strain gages. Absolute extrinsic Fabry-Perot interferometric sensors, capable of measuring absolute displacement and strain, were embedded in a steel-reinforced concrete specimen. Loading experiments performed on this specimen also yielded absolute strain information. The specimen was cyclically loaded for more than 100000 cycles in this geometry and the sensors still provided quantitative strain information regarding this specimen.

Journal ArticleDOI
TL;DR: In this article, an extrinsic sapphire fiber-based sensor is proposed for use in high-temperature environments, including the processing environments of advanced hightemperature materials and the in-situ operational environments of high temperature adaptive materials and structures.
Abstract: Describes the development and testing of an extrinsic sapphire fiber-based sensor design intended for use in high-temperature environments, including the processing environments of advanced high-temperature materials and the in-situ operational environments of high-temperature adaptive materials and structures. In this sensor, a length of uncoated, unclad, single-crystal optical-quality multimode sapphire fiber is fusion-spliced to a single-mode silica fiber. Another sapphire fiber is placed end-to-end with the first sapphire fiber, so that the two adjacent end-faces of the sapphire fibers form a low-finesse Fabry-Perot cavity. This sensor is demonstrated to be useful for both strain and temperature measurement, with a 10-microstrain resolution over a range of 0-1150 microstrain, and a 3.5 degrees C temperature resolution over a range from 150 to 650 degrees C.

Journal ArticleDOI
TL;DR: The rationale for neural network-based control is outlined, a brief description of the analytical and experimental investigations, and illustrative numerical examples are given of control of a non-linear single-degree-of-freedom structure by neural net.
Abstract: Active control of structures against environmental loads such as those due to wind and earthquakes has received much attention recently. Feasibility studies, numerical and experimental, have shown that it is a viable alternative to conventional methods in enhancing the performance of structures under such loadings. Most of the research thus far has concentrated on developing mathematical models and algorithms based on optimal control theory and the necessary hardware to implement the control. Research on control based on neural networks has been very limited in spite of the potential advantages of this method such as its inherent ability to handle nonlinear systems, incorporate leads or delays, and recover from partial system failure. This paper presents a method of control of structures based on neural networks. The rationale for neural network-based control is first outlined, followed by a brief description of the analytical and experimental investigations, and finally illustrative numerical examples are given of control of a non-linear single-degree-of-freedom structure by neural net.

Journal ArticleDOI
Ron Barrett1
TL;DR: In this paper, the structural and aerodynamic characteristics of a new class of active flight control surface are presented, which uses a symmetric, subsonic aerodynamic shell which is supported at the quarter-chord by a main spar and actively pitched by an adaptive torque-plate.
Abstract: The structural and aerodynamic characteristics of a new class of active flight control surface are presented. This new type of surface uses a symmetric, subsonic aerodynamic shell which is supported at the quarter-chord by a main spar and actively pitched by an adaptive torque-plate. The structural mechanics of the torque-plate and several actuator elements are detailed, including newly invented interdigitated electrode (IDE) and constrained directionally attached piezoelectric (CDAP) elements. Laminated plate models demonstrate that both generate similar deflections with comparable torsional stiffness. An experimental torque-plate specimen constructed from PSI-5A-S2 piezoceramic shows high torsional deflections and stiffness as well as excellent correlation with theory. The constrained torque-plate was integrated into a 12.5 cm span *5 cm chord adaptive missile fin which was designed for Mach 0.6 flight under standard conditions. The specimen showed static pitch deflections up to +or-8.1 degrees and dynamic deflections of +or-19 degrees at resonance. The active surface was also wind tunnel tested up to 40 m s-1 and demonstrated invariant pitch deflections as a function of airspeed, a steady break frequency of 50 Hz, no flutter, buffet or divergence tendencies and steady lift coefficient changes up to +or-0.51.

Journal ArticleDOI
TL;DR: In this article, an optimization of the geometry and the excitation voltage applied to a piezoelectric actuator embedded on a plate structure is studied to reduce the radiation of sound into the space above the plate when the plate is excited by the acoustic pressure field produced by a noise source located below the plate.
Abstract: Optimization of the geometry and the excitation voltage applied to a piezoelectric actuator embedded on a plate structure is studied to reduce the radiation of sound into the space above the plate when the plate is excited by the acoustic pressure field produced by a noise source located below the plate. In the more realistic case, one could consider the plate to comprise of one wall of an enclosure containing a noise source. Finite element modeling is used for the plate structure that includes a full description of coupled fields in the piezoelectric actuator and elastic plate. Since the use of three-dimensional (3D) elements in the plate structure tends to stiffen the structure unnecessarily, a combination of shell elements for the plate and 3D elements for the actuator with transition elements to connect the two regions have also been implemented. Clamped boundary conditions are assumed in the calculations. The cost function of optimization is the sound energy radiated onto a hemispherical surface of given radius and the optimization parameters are size of the piezoelectric actuator as well as the amplitude and phase of the voltage applied to the actuator. Good results are obtained for both resonance and off-resonance conditions. The optimization is robust enough that even if the pattern of the acoustic pressure field changes, the radiated sound is still minimized.

Journal ArticleDOI
TL;DR: In this article, an experimental and finite-element study of the optomechanical response of a diametrically loaded Bow-Tie high-birefringent optical fiber was performed.
Abstract: This paper describes an experimental and finite-element study of the optomechanical response of a diametrically loaded Bow-Tie high-birefringent optical fiber. The thermomechanical finite-element analysis performed in this study uses PATRAN as the solid modeler and ABAQUS as the analysis package. The purpose of this study is to determine the effect of a diametrical load on the optical phase generated by polarimetric sensors as a function of polar angle. This is done in order to understand the behavior of structurally embedded polarimetric sensors, and to determine the effect of load-induced rotation of principal optical axis in a Bow-Tie fiber in order to assess the response of the lead-sensitivity of lead-insensitive embedded polarimetric sensor configurations. The results indicate that the stress concentrations produced by the stress-applying parts are responsible for a polarimetric phase sensitivity that is a function of the applied load direction. The results further indicate that the diametric loads do not significantly alter the principal optical axes in the lead-in fiber.

Journal ArticleDOI
TL;DR: In this paper, a simulation is carried out on the vibration control of the cylindrical shell by using distributed piezoelectric actuators, which produces a bending moment or an in plane force when pulse voltages are applied synchronously with the pulse current of the coils.
Abstract: One major problem in magnetic resonance image (MRI) equipment is the high-level noise borne by the vibration of the cylindrical shell to support the coils for gradient magnetic fields. The vibration of the shell is excited by the Lorentz force between the pulse current applied to the coils and the main magnetic field. In order to suppress the noise inside the cylindrical shell, it is aimed to control the vibration of the shell. In this paper, simulation is carried out on the vibration control of the shell by using distributed piezoelectric actuators. The actuators produce a bending moment or an in plane force when pulse voltages are applied synchronously with the pulse current of the coils. Coupling of actuators and vibration modes, and parameter optimization are also discussed. The simulation results show that the vibration level is successfully reduced in the frequency range of 400-1200 Hz.

Journal ArticleDOI
TL;DR: In this paper, the authors explored the possibility of using neural techniques to detect the presence of structural faults from dynamic response data in simple structures of practical interest for structural engineering and proposed some techniques of structural response signal processing and analysis devised for the purpose of improving the diagnostic capabilities of connectivistic methods through numerical experiments.
Abstract: This study explores the possibility of using neural techniques to detect the presence of structural faults from dynamic response data in simple structures of practical interest for structural engineering. Some techniques of structural response signal processing and analysis devised for the purpose of improving the diagnostic capabilities of connectivistic methods are proposed through numerical experiments. To this end, cross-correlations between dynamic response signals are used as inputs for hierarchically organized networks which are able to assess and locate structural damage in numerical models. The satisfactory results obtained are discussed and explained with the aid of projections of the multi-dimensional decision space through the use of simple `grow and learn` neural models.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model was developed to predict whether or not intelligent constrained-layer (ICL) damping treatments could simultaneously reduce bending and torsional vibrations of composite beams having bending-torsion coupling stiffness.
Abstract: This paper aims to develop a mathematical model to predict whether or not intelligent constrained-layer (ICL) damping treatments could simultaneously reduce bending and torsional vibrations of composite beams having bending-torsion coupling stiffness. The ICL composite-beam model is obtained by integrating the existing ICL composite-plate model proposed by Shen (1994). When the plate width (along the x-axis) is much smaller than the plate length (along the y-axis), integration of the ICL composite-plate equations and linearization of displacement fields with respect to x will lead to a set of equations that couple bending, torsional, and axial vibrations of a composite beam. The equations of motion and associated boundary conditions are normalized and rearranged in a state-space matrix form, and the vibration response is predicted through the transfer function approach developed by Yang-Tan (1992). A numerical example is illustrated on a composite beam with bending-torsion coupling stiffness.

Journal ArticleDOI
TL;DR: In this paper, the authors performed nonlinear, quasi-static finite-element calculations for multilayered, electrostrictive, ceramic actuators using a fully coupled constitutive law for electrostriction which uses strain and polarization as independent state variables.
Abstract: Nonlinear, quasi-static finite-element calculations are performed for multilayered, electrostrictive, ceramic actuators. Both a stand-alone device and an array of devices embedded in a 2-2 composite are studied. The numerical model is based on a fully coupled constitutive law for electrostriction which uses strain and polarization as independent state variables. This law accounts for the stress dependence of the ceramic`s dielectric behavior and simulates polarization saturation at high electric fields. Two-dimensional plane strain computations are performed for a single actuator constructed from Pb(Mg13/Nb23/)O3-PbTiO3-BaTiO3(PMN-PT-BT). The stress state near an internal electrode tip is computed and a fracture mechanics analysis is performed to assess the device`s reliability. The effect of compressive prestress on the actuator`s induced strain response is also predicted. In a second problem, a 2-2 composite embedded with an array of PMN-PT-BT multilayered actuators is studied with plane stress and plane strain versions of the finite-element technique. A unit cell model containing a single actuator is used to predict the displacement distribution at the surface of the composite under various levels of electric excitation.

Journal ArticleDOI
TL;DR: In this paper, the influence of nonlinear properties of filler material on the resulting dielectric properties has been studied both theoretically and experimentally, using effective medium theory to show how much of the nonlinearity of the filler is transferred to the composite.
Abstract: Polymer composites with high dielectric constant are widely used as shielding and field grading materials. An improvement of the refractive grading can be expected for a dielectric constant being a nonlinear function of the electric field or the temperature, as known for nonlinear resistive field grading. An increase of the dielectric constant in those areas where the highest electrical field occur will result in a homogenization of the field distribution. Such composite materials can be considered as having the smart functions of sensing and actuating. The influence of nonlinear properties of filler material on the resulting dielectric properties has been studied both theoretically and experimentally. Calculations using effective medium theory show how much of the nonlinearity of the filler is transferred to the composite. They are compared with experiments on composites containing ferroelectric, semiconducting and varistor-type filler material in a thermoset or thermoplastic matrix. Depending on the filler type, the dielectric constant increases by a factor of up to three, for example, on raising the temperature from 30 degrees C to 150 degrees C. Such an enhancement can be sufficient to rearrange the field distribution in stressed insulating parts.

Journal ArticleDOI
TL;DR: In this paper, a novel technique for effective detection of edge-induced and local internal delamination caused by cyclic loading of composite materials is proposed by employing the highly sensitive extrinsic Fabry-Perot interferometric optical fiber-based sensor for detecting discontinuities along the composite transverse axis.
Abstract: A novel technique for effective detection of edge-induced and local internal delamination caused by cyclic loading of composite materials is proposed This scheme employs the highly sensitive extrinsic Fabry-Perot interferometric optical fiber-based sensor for detecting discontinuities along the composite transverse axis Sensors in surface-mounted and completely embedded configurations provide real-time, on-line information about damage initiation and propagation within the composite This method is extended to monitoring delamination between pairs of off-axis plies by employing path-matching multiplexing of conventional EFPI sensors in a white light interferometry configuration Such multiple-sensor-element in situ monitoring may increase the probability of detection of flaws of critical size that may lead to premature structural failure

Journal ArticleDOI
TL;DR: In this paper, an experimental and analytical study of a controllable electrorheological (ER) device configured to induce an adjustable amount of dynamic shear force in response to an applied voltage is presented.
Abstract: This paper presents some of the results of an experimental and analytical study of a controllable electrorheological (ER) device configured to induce an adjustable amount of dynamic shear force in response to an applied voltage. Maps of the force-deformation characteristics of the aluminosilicate based ER material are developed over a relatively wide frequency range, and approximating analytical expressions are obtained for the force-deformation-frequency-voltage characteristics of the material. Subsequently, an evaluation is made of the efficiency of using online control of an electrorheological actuator to emulate the operation of an optimally tuned auxiliary mass damper attached to a primary system subjected to arbitrary dynamic environments. It is shown through numerical simulation studies that the proposed parameter control algorithm provides an efficient means for the online control of the primary system under a wide range of excitations. An experimental study is presented in which an ER device is used, in conjunction with a small laboratory building model, as a semiactive element in an online structural control approach using pulse control techniques.

Journal ArticleDOI
TL;DR: In this paper, a higher-order performance criterion is introduced and an optimal nonlinear feedback control law is derived based upon this criterion and it is shown that this nonlinear control law can significantly improve peak response reduction under the same constraints imposed on the control resources as in the linear quadratic regulator case.
Abstract: The linear quadratic regulator has been used extensively in many control systems designed for structural control applications due to its stability and robustness. Recent results obtained from simulation, model experiments, and full-scale structural applications, however, show that it is difficult to employ linear feedback control laws to produce a significant peak response reduction when the peak response occurs during the first few cycles of the time history. In this paper, based on the fact that minimizing the maximum response can be approximated by minimizing a higher-order performance index, a higher-order performance criterion is introduced and an optimal nonlinear feedback control law is derived based upon this criterion. It is shown that this nonlinear control law can significantly improve peak response reduction under the same constraints imposed on the control resources as in the linear quadratic regulator case.

Journal ArticleDOI
TL;DR: In this paper, the dynamic behavior of an electrorheological (ER) material based adaptive beam was modeled and the structural model of the assembly in a transverse continuous vibration mode subjected to simply-supported boundary conditions and actuation at a single point on the adaptive beam surface was analyzed.
Abstract: The use of electrorheological (ER) materials in adaptive structures has received much attention. Adaptive structures are based on controlling the pre-yield rheology of ER materials, which is achieved by applying different electrical fields. In this study the dynamic behavior of an ER material based adaptive beam was modeled. The beam was composed to three layers: an ER material controllable damping layer and surrounding upper and lower elastic plates. The structural model of the assembly in a transverse continuous vibration mode subjected to simply-supported boundary conditions and actuation at a single point on the adaptive beam surface was analysed. The model was tested under the conditions of varying forcing frequency from 0-300 Hz, and applied electrical field from 0-35 kV mm-1. The analytical results are compared with experimental results under the same physical conditions. Qualitative agreement between theory and experimentation resulted. In addition an effect was made to reduce the vibration of the structure by selecting the optimum electrical field which yields minimized vibration for each frequency. Continuing efforts towards further understanding the behavior of ER material based adaptive structures are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors used finite element techniques to analyse the mechanical stress and strain concentrations in and around an optical fiber embedded in a composite laminate and failure analysis was performed.
Abstract: Advanced finite element techniques are used to analyse the mechanical stress and strain concentrations in and around an optical fibre embedded in a composite laminate. The models represent many features observed in real materials with embedded optical fibres. Three general laminate constructions were analysed with the optical fibre at the mid-plane and near the laminate surface. The models represent test coupons that are used to measure the effects of the embedded optical fibre on the laminate strength in tension and flexure; the applied loads and boundary conditions reflect these tests. Failure analysis is performed.